/**
 * <p>系统名称：Web_Rich</p>
 * <p>业务名称: Base64  </p>
 * <p>概要说明：业务的机能概要。</p>
 * @author: zhouxiaoyan   
 * @date: 2011-9-14 上午09:37:22
 * @version 1.0.1
 * 更新时间:  
 * 更改内容：    
 * 最后更新者： 
 */
package com.yzy.tool
{
	
	　　import flash.utils.ByteArray;
	
	　　public class Base64 {
		
		　　private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
		
		　　public static const version:String = "1.0.0";
		
		　　public static function encode(data:String):String {
			
			　　// Convert string to ByteArray
			
			　　var bytes:ByteArray = new ByteArray();
			
			　　bytes.writeUTFBytes(data);
			
			　　// Return encoded ByteArray
			
			　　return encodeByteArray(bytes);
			
		　　}
		
		　　public static function encodeByteArray(data:ByteArray):String {
			
			　　// Initialise output
			
			　　var output:String = "";
			
			　　//Create data and output buffers
			
			　　var dataBuffer:Array;
			
			　　var outputBuffer:Array = new Array(4);
			
			　　// Rewind ByteArray
			
			　　data.position = 0;
			
			　　// while there are still bytes to be processed
			
			　　while (data.bytesAvailable > 0) {
				
				　　// Create new data buffer and populate next 3 bytes from data
				
				　　dataBuffer = new Array();
				
				　　for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++) {
					
					　　dataBuffer[i] = data.readUnsignedByte();
					
				　　}
				
				　　// Convert to data buffer Base64 character positions and
				
				　　// store in output buffer
				
				　　outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;
				
				　　outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4);
				
				　　outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6);
				
				　　outputBuffer[3] = dataBuffer[2] & 0x3f;
				
				　　// If data buffer was short (i.e not 3 characters) then set
				
				　　// end character indexes in data buffer to index of '=' symbol.
				
				　　// This is necessary because Base64 data is always a multiple of
				
				　　// 4 bytes and is basses with '=' symbols.
				
				　　for (var j:uint = dataBuffer.length; j < 3; j++) {
					
					　　outputBuffer[j + 1] = 64;
					
				　　}
				
				　　// Loop through output buffer and add Base64 characters to
				
				　　// encoded data string for each character.
				
				　　for (var k:uint = 0; k < outputBuffer.length; k++) {
					
					　　output += BASE64_CHARS.charAt(outputBuffer[k]);
					
				　　}
				
			　　}
			
			　　// Return encoded data
			
			　　return output;
			
		　　}
		
		　　public static function decode(data:String):String {
			
			　　// Decode data to ByteArray
			
			　　var bytes:ByteArray = decodeToByteArray(data);
			
			　　// Convert to string and return
			
			　　return bytes.readUTFBytes(bytes.length);
			
		　　}
		
		　　public static function decodeToByteArray(data:String):ByteArray {
			
			　　// Initialise output ByteArray for decoded data
			
			　　var output:ByteArray = new ByteArray();
			
			　　// Create data and output buffers
			
			　　var dataBuffer:Array = new Array(4);
			
			　　var outputBuffer:Array = new Array(3);
			
			　　// While there are data bytes left to be processed
			
			　　for (var i:uint = 0; i < data.length; i += 4) {
				
				　　// Populate data buffer with position of Base64 characters for
				
				　　// next 4 bytes from encoded data
				
				　　for (var j:uint = 0; j < 4 && i + j < data.length; j++) {
					
					　　dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));
					
				　　}
				
				　　// Decode data buffer back into bytes
				
				　　outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);
				
				　　outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);
				
				　　outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];
				
				　　// Add all non-padded bytes in output buffer to decoded data
				
				　　for (var k:uint = 0; k < outputBuffer.length; k++) {
					
					　　if (dataBuffer[k+1] == 64) break;
					
					　　output.writeByte(outputBuffer[k]);
					
				　　}
				
			　　}
			
			　　// Rewind decoded data ByteArray
			
			　　output.position = 0;
			
			　　// Return decoded data
			
			　　return output;
			
		　　}
		
		　　public function Base64() {
			
			　　throw new Error("Base64 class is static container only");
			
		　　}
		
	　　}
	
　　}